Highly water-absorbent polymers are widely used in a wide range of applications, particularly as materials for retaining human waste, such as disposable diapers. In existing types of disposable diapers, however, highly water-absorbent polymers are used together with paper and other natural and synthetic fibrous materials, and usually covered with a polyolefin or other synthetic resin film. This makes it difficult to dispose of such materials after use by landfill and other disposal means because of their un-biodegradability. To cope with this, used disposable diapers are, after collection, usually incinerated using incinerators in a high cost operation, without being subjected to any pretreatment, such as dehydration, as reported in a meeting of the Medical Waste Disposal Study Group held on Dec. 1, 1990 (Kenichi Miyashita, "Proper Disposal of Sanitary Materials and Other Solid Wastes--Incinerating Tests of Used Paper Diapers," Summary of Lectures Presented Before the 6th Medical Waste Study Group Seminar, UniCharm, Co., Ltd.)
Incineration of sanitary waste material in the commonly used types of incinerators, however, has frequently caused various problems, such as offensive odor or incomplete combustion in a number of municipal waste incinerating plants, because the high water content of such waste tends to lower the temperature in the incinerator. To reduce such problems, most municipal waste incinerating plants use a large amount of oil and other auxiliary fuels to raise the temperature in the incinerator. This leads not only to increased incinerator cost but also to increased incinerating fuel cost. In addition, the increased volume of disposable diapers due to swelling as a result of water absorption causes incinerating efficiency to lower.